The present invention relates to a subject judgment program for letting a computer, microprocessor, etc. function as a judging device that judges the type of a subject in an image formed by image data. The invention also relates to a digital camera which employs the subject judgment function to control an image capturing process and/or a quality correction process for correcting image data obtained or to be obtained by shooting a subject in accordance with the type of the subject.
As is commonly known, image data for displaying an image of a subject is generated when the subject is shot by a digital camera or when a positive/negative image containing the subject is read by a scanner, and the brightness, sharpness, color, etc. of the image formed by the image data can be changed by executing mathematical operations to the image data. Therefore, even when the quality of the image is not fine due to the settings/characteristics of the digital camera/scanner or the lighting on the subject, the image quality can be corrected easily only by executing proper computation to the image data.
Image processing software installed in digital cameras in recent years generally has such an image quality correction function. However, users having little experience in image quality correction do not understand which type of image quality correction process should be applied to the image data depending on the type of the subject in the image. Therefore, some of the many types of image processing software have the function of judging the type of the subject in the image formed by the image data in order to automatically execute the image quality correction during shooting or to inform the operator (user) of the type of the subject so that the operator can confirm the judgment is made correctly. An example of such process is described in Japanese Patent Provisional Publication No. 2003-018453.
However, the conventional image processing software described above is configured to judge the type of the subject based on setting/operational information obtained from each device in the digital camera such as a distance to the subject and a focal length and magnification of the lens used for shooting. Such a judgment may not be reliably correct since various subjects can be photographed at various operational settings.
It may be possible to introduce a so-called “matching technique” as a method for correctly judging the subject in the image. In this case, a lot of pieces of image data (images) of a variety of subjects are prepared as reference image data (reference images), and when image data of a subject image (as the target of image quality correction) is input, characteristic values of the subject image are compared with those of each reference image to obtain a difference regarding the characteristic values, and one of the reference images giving the smallest difference is identified. By such a process, the subject in the subject image is judged to be identical with the subject in the identified reference image.
In such a conventional method, in order to make the judgment as correct as possible, a large number of pieces of reference image data (reference images) may be prepared, and comparison of the input image and each of the reference images should be performed precisely.
However, digital cameras (especially, compact digital cameras) have certain limitations in storage capacity and processing speed for the image processing. Therefore, if the conventional matching process is performed, it takes a very long time for judgment, keeping the operator waiting for the completion of the judgment on the subject in the image. If the waiting time is shortened, the results may be unreliable.